1. Field of the Invention
This invention relates to a method and an apparatus for cutting a glass material.
2. Related Background Art
A glass material melted in a furnace is adjusted in temperature to a value necessary to form a desired glass product, is transferred to and discharged from a glass material reservoir called a spout, is cut into a mass of glass (gob) having a predetermined size, and is supplied to a forming apparatus. To cut the glass material to a predetermined size, a cutting apparatus, having a cutter blade, is provided beneath an orifice provided in the lower portion of the spout.
In a conventional glass material cutting apparatus used in a glass forming apparatus such as a bottle manufacturing apparatus or the like, arms provided with left and right cutting blades are opposed to each other and are moved along arc-shaped tracks or linear tracks to come close to or away from one another in order to cut the glass material (see, e.g., Japanese Kohyo No. 10-511633 and, in particular, pages 4 and 5, FIGS. 1 and 2 thereof). However, to satisfy a current need for a high-speed manufacturing, the temperature of the glass material is increased to thereby reduce the viscosity so that the cutting blades can be moved at a high-speed. However, due to this solution to enhance the productivity, the following problems have been raised.
For example, in a cutting apparatus in which arms having cutting blades are opened and closed by an arcwise movement (this type of apparatus is currently most popular), if an opening and closing cycle of the arm is shortened, the cutting blades provided on the arms cannot be completely closed so that the glass material fails to be cut completely, and therefore, stringing of the glass gob or interconnection of glass gobs like a string of sausages occurs.
In a cutting apparatus in which the cutting blades of the arms are opened and closed by an arcwise movement, the distal portions of the cutting blades close to the pivotal fulcrums of the opening and closing arms come into contact with the glass material earlier and separate therefrom later. On the other hand, the proximal portions of the cutting blades distant from the fulcrums of the opening and closing arms come into contact with the glass material later and separate therefrom earlier. This causes a difference in the temperature or instability of the shape of cutting surface portions of the glass material in contact with the cutting blades, due to a difference in the contact time of the cutting blades. This tendency is particularly remarkable in a cutting apparatus in which a plurality of cutting blades are provided in the axial direction of the arms, and thus resulting in unstable quality of the glass gobs.
Furthermore, in any type of cutting apparatus in which the cutting blades are opened and closed with respect to a glass material by an arcwise movement or translation, if the temperature is increased to reduce the viscosity of the glass material in order to respond to a need for a high-speed manufacturing, a so-called “banana shaped gob phenomenon” in which a soft glass material having a low viscosity rides on the upper surfaces of the cutting blades and is moved together therewith and is bent in the same direction as the movement of the cutting blades tends to occur when the glass material is cut. If this phenomenon occurs, the glass material tends to be minutely damaged at its lower portion or to have a non-uniform temperature distribution, thus leading to deterioration of the quality of the product.